1. Technical Field
The present invention relates to test instruments for electrical networks and devices, including network analyzers and other precision transceivers.
2. Background
Historically, many upper millimeter-wave systems have been run with no power control other than that provided by an attenuator and/or saturation of frequency multipliers. The lack of control is often a result of a lack of suitable direct detectors with sufficient dynamic range. The inability to control power prevents power sweeps for device under test compression and other linearity-related measurements, and results in relatively unstable power over time. The control range of the power may also be limited due to stability of the attenuator response.
One approach to controlling power includes leveling the input drive to a millimeter-wave multiplier or multiplier chain. However, because of the relative instability of multipliers themselves (particularly higher order multipliers), the output power at millimeter-wave frequencies can be somewhat unstable. This can cause problems with device modeling measurements where variation in instantaneous power can affect multiple model elements.
Another approach has been to use a post-processed receiver signal to, at a software level, adjust the power setting to return that same processed signal to a nominal value. Because of the many layers of processing, this loop response tends to be very slow and likewise leads to large instantaneous power variations and potential measurement errors of sensitive devices.
What is needed are real-time or near real-time systems and methods for measuring high frequency response of a device under test having improved power leveling.